The design of a feedback circuit is one of the more difficult tasks a circuit designer can undertake. In a standard feedback circuit, the designer may adjust components to control the behavior of a system. However, sometimes a feedback circuit includes integrated circuits. These integrated circuits have many, if not hundreds, of internal components. The values of the internal components, as well as the frequency characteristics of these integrated circuits are fixed. This limits the designer's degree of freedom to manipulate the frequency response of the circuit.
One example of this problem exists in the field of power supply design. Power supply circuits sometimes include optocouplers and integrated controllers, switches, and noise filters. The addition of these components greatly restricts the designer's ability to achieve desired frequency characteristics. Furthermore, power components are typically not adjustable due to certain input/output specifications imposed on the designer. While there are known ways to design stable control loops with the above constraints, they typically result in a less than desirable phase margin. Improving the phase margin while maintaining the desired frequency response typically involves a complete redesign of the feedback circuit, resulting in increased time and cost.